A. Technical Field
The present invention relates to integrated circuits, and more particularly, to systems, devices and methods of detecting a shock or a disturbance experienced by a gyroscope and differentiating rotation-based sense signals from noises introduced by the shock or disturbance.
B. Background of the Invention
A microelectromechanical structure (MEMS) is widely applied as a sensor to measure acceleration, rotation, pressure and many other physical parameters. The MEMS device is normally formed on a silicon substrate using a micromachining process, adopts characteristic feature sizes of several micrometers, and transduces mechanical movement to electrical signals that may indicate the level of an interested parameter. In particular, MEMS-based gyroscope devices have been developed and applied to monitor rotational rates of the devices with respect to certain axes, and a multitude of consumer and automotive applications have successfully adopted such MEMS-based gyroscope devices. For instance, many automotive integrate the gyroscope devices for vehicle stability control, navigation assist, load leveling/suspension control, collision avoidance and roll over detection.
Conventional MEMS-based gyroscope devices use vibrational mechanical elements (proof masses) to sense a rate of rotation. FIG. 1A illustrates a mechanical element 100 disposed in a rotating reference frame. The mechanical element 100 is driven to oscillate in a first orthogonal axis (x-axis), and as the frame rotates with respect to a second orthogonal axis (y-axis), vibratory movement is induced along the third orthogonal axis (z-axis) due to Coriolis acceleration. A corresponding inertial Coriolis force FC may be represented as:FC=−2Ωmv  (1)where Ω is the rate of rotation, m is the mass of the mechanical element 100 and v is the vibrational velocity along the first orthogonal axis.
FIG. 1B illustrates an exemplary vibratory gyroscope device 150 that relies on electrostatic actuation and capacitive sensing to detect the Coriolis force. A proof mass 152 is driven to vibrate along an x-axis by comb drivers 154 arranged at two opposing sides. A capacitor is formed between the substrate and the proof mass 152. In response to rotation with respect to a y-axis, the proof mass 152 vibrates towards and away from a substrate that the gyroscope device 150 is situated on, and therefore, the gap distance of the capacitor varies, leading to a capacitive variation that is associated with the Coriolis force. An interface readout circuit is normally integrated with the gyroscope device 150 to convert this capacitive variation to a gyroscope sense signal that is related to the magnitude of the Coriolis force and therefore to the corresponding rate of rotation.
Although the gyroscope sense signal includes interested information related to the rate of rotation, noises are also introduced by various shock and disturbance sources and could significantly compromise the accuracy of rotation sensing. Particularly in automotive applications, shock robustness is critical and constitutes a key characteristic, because strict safety constraints have to be imposed to ensure a failsafe and robust system. In such a context, an occurrence of shock or disturbance needs to be flagged and used to indicate that an unreliable and unpredictable rate signal is outputted, when the level of the shock or disturbance exceeds a threshold value tolerable by a corresponding rotation sensing system. Many existing gyroscope devices in the market have adopted sensor or package solutions to improve shock robustness of the devices themselves. However, none of them flags the occurrence of shock or disturbance with respect to a certain tolerance, and warns a host to take suitable countermeasures.